Thermally enhanced package for an integrated circuit

ABSTRACT

A circuit assembly having an insulating base, heat-conducting plate and circuit containing die is disclosed. The die is in thermal contact with the heat-conducting plate, which is bonded to the insulating base. The insulating base includes heat-conducting channels that are in thermal contact with the heat-conducting plate. The die includes an integrated circuit therein and is mounted such that the heat-conducting plate is disposed between the die and the insulating plate. The insulating base preferably includes signal conducting channels for providing electrical connections to the die, the heat-conducting plate having an opening therein for making the connections between the die and the conducting channels. The assembly may also include a heat-spreading cover in thermal contact with the heat-conducting base plate, the heat-spreading cover overlying the die. The heat-conducting channels are preferably filled with solder, and include a solder protrusion extending from the heat-conducting channels.

FIELD OF THE INVENTION

[0001] The present invention relates to packages for integrated circuitsand the like.

BACKGROUND OF THE INVENTION

[0002] Semiconductor chips are typically sealed in a package that issoldered to a printed circuit board. The various connections between theelectrical components on the chip and the conductors on the printedcircuit board are made through conductors that pass through the packageand are connected to the printed circuit board by solder. Within thepackage, the chip is encapsulated in a potting compound that protectsthe chip from damage caused by exposure to moisture and oxygen.

[0003] Early chip designs contained relatively few active componentsoperating at relatively slow speeds, and hence, heat dissipation was nota major problem. However, as chip speeds and component densities haveincreased, heat dissipation has become a major problem. One prior artmethod for increasing the heat dissipation in a semiconductor packageutilizes a heat-conducting cover. In this design, the cover is placedover the encapsulated chip to improve the heat conduction from the chipto the air above the chip. Unfortunately, this approach is of limitedvalue since the heat dissipating cover depends on the conduction of theheat from the chip through the encapsulating material, which is a poorheat conductor. In addition, the surface area of the cover is limited tothe size of the semiconductor package, and hence, the amount of heatthat can be dissipated by the cover is limited.

SUMMARY OF THE INVENTION

[0004] The present invention is a circuit assembly having an insulatingbase, heat-conducting plate and circuit-containing die. The die is inthermal contact with the heat-conducting plate, which is bonded to theinsulating base. The insulating base includes heat-conducting channelsthat are in thermal contact with the heat-conducting plate. The dieincludes an integrated circuit therein and is mounted such that theheat-conducting plate is disposed between the die and the insulatingplate. The insulating base preferably includes signal conductingchannels for providing electrical connections to the die, theheat-conducting plate having an opening therein for making theconnections between the die and the conducting channels. The assemblymay also include a heat-spreading cover in thermal contact with theheat-conducting base plate, the heat-spreading cover overlying the die.The heat-conducting channels are preferably filled with solder, andinclude a solder protrusion extending from the heat-conducting channelsto facilitate attachment to a printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a top view of semiconductor package according to oneembodiment of the present invention.

[0006]FIG. 2 is a cross-sectional view of package 10 through line 21-22.

[0007] FIGS. 3-5 are cross-sectional views of the packaged chip atvarious stages in the packaging process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0008] The manner in which the present invention provides its advantagescan be more easily understood with reference to FIGS. 1 and 2. FIG. 1 isa top view of semiconductor package 10 with a portion of the topheat-conducting plate cut away. FIG. 2 is a cross-sectional view ofpackage 10 through line 21-22. Semiconductor package 10 includes asemiconductor chip 15 that is mounted on a heat-conducting plate 12.Plate 12 is preferably constructed from copper. Heat-conducting plate 12is bonded to a substrate 14 by a layer of adhesive 13. Substrate 14 hasa number of holes running therethrough. Some of these holes are utilizedfor making connections to the ground place of a printed circuit board onwhich package 10 is to be mounted. These connections are made by solderballs that are heated when the package is mounted to the printed circuitboard. Exemplary holes of this type together with the solder balls areshown at 18.

[0009] Signal connections between chip 15 and the printed circuit boardare made through a copper plated holes in substrate 14 that connect padson the top and bottom surface of substrate 14. Exemplary signalconducting paths are shown at 32. The pads 17 on chip 15 and thecorresponding signal paths 32 on substrate 14 are connected viaconventional wire bonding techniques. Exemplary wire bonds are shown at16.

[0010] A heat-conducting top plate 19 may also be incorporated in thepackage to further dissipate heat generated by chip 15. If such a plateis included, it is preferably connected to heat-conducting plate 12 atthe periphery of heat-conducting plate 12 and forms a “roof” over chip15. However, embodiments lacking top plate 19 can be advantageouslyutilized. The space 11 between top plate 19 and chip 15 is filled with aconventional encapsulating compound to protect chip 15 from damage. Iftop plate 19 is omitted, this encapsulating layer is still utilized toprotect the chip. An additional layer of molding compound can beincluded around the periphery of top plate 19; however, to simplify thedrawing, this additional layer of molding compound has been omitted fromthe drawings.

[0011] The present invention can dissipate substantially more heat thanprior art packages because the heat-conducting plate is more efficientin removing the heat from chip 15 and because the heat so removed ischanneled to a larger heat dissipating surface. Heat-conducting plate 12has a higher thermal conductivity then the conventional packagingmaterial on which the chip is normally mounted in prior art devices. Inaddition, heat-conducting plate 12 is thermally connected to the groundplane on the printed circuit board via the heat-conducting plugs shownat 18. These heat-conducting plugs are preferably constructed fromsolder that “wets” the copper from which plate 12 is constructed. Hence,heat collected by heat-conducting plate 12 is effectively channeled tothe ground plane of the printed circuit on which package 10 is mounted.Since the ground plane of the circuit board has considerably moresurface area exposed to the air than chip 15 or top 19, heat can be moreeffectively transferred to the air above the ground plane provided theheat-conducting plugs have sufficient combined cross-sectional area toassure that the plugs do not inhibit the flow of heat to the groundplane. In optimize the heat transfer area, the heat-conducting plate isslightly smaller than substrate 14. In the preferred embodiment of theinvention, the heat-conducting plate has dimensions that are 0.5 mmsmaller than substrate 14.

[0012] In addition, heat from the heat-conducting plate is routeddirectly to top plate 19, which also has a surface area that issubstantially larger than chip 15. It should be noted that the presentinvention, unlike prior art schemes, does not depend on the heat fromthe chip traversing the encapsulating compound above the chip, andhence, the thermal “bottleneck” that hampers prior art designs issubstantially reduced in the present invention. In the preferredembodiment of the invention, the heat conducting channels are between0.5 mm and 0.65 mm to assure that these channels do not limit the heatflow from the chip to the ground plane of the printed circuit board.However, the sizes and numbers of heat-conducting channels can beadjusted to match the heat output of the chip.

[0013] The manner in which the semiconductor chip is packaged using thepresent invention may be more easily understood with reference to FIGS.3-5, which are cross-sectional views of the packaged chip at variousstages in the packaging process. Referring to FIG. 3, in the preferredembodiment of the present invention, the packaging process starts with apart in which the heat-spreading plate 51 is already attached to asubstrate 54 by an adhesive layer 52. It is assumed that vias 57 havebeen drilled through the substrate to the heat-spreading plane.

[0014] Chip 60 is then attached to heat spreader 51 and the wire bonds61 between chip 60 and the signal pins 53 in the substrate are formedusing a conventional wire bonding system. If the optional top heatdissipating plate 62 is to be used, it is attached to heat-spreadingplate 51 leaving the package as shown in FIG. 4.

[0015] A conventional molding process is then used to encapsulate all ofthe components in an encapsulating layer 65. The vias 57 are then filledwith small solder balls using a conventional drop in process and thesubstrate is then heated to melt the solder balls leaving the drilledholes filled with solder. Finally, solder balls 66 are attached to thevarious vias and copper pads leaving the package as shown in FIG. 5. Itis assumed that the above-described operations are performed on a stripof packages, not just the one shown in the figures. In the final step,the individual packages are separated using a conventional singulationprocess.

[0016] In the above-described embodiments of the present invention, theheat from the chip is conducted away from the chip both by utilizing theoptional heat dissipating plate and the conducting paths to the groundplane of the underlying printed circuit board. While the paths throughthe substrate to the ground plane can provide substantially more heatconducting capacity than the top heat dissipating plate 62, thecombination of the heat conducting plate under the chip and the top heatdissipating plate still provides substantially better heat conductionthan prior art methods. Accordingly, if the top heat-conducting plate isused, the heat conducting vias may be omitted in cases in which the heatgenerated by the chip is less intense.

[0017] Various modifications to the present invention will becomeapparent to those skilled in the art from the foregoing description andaccompanying drawings. Accordingly, the present invention is to belimited solely by the scope of the following claims.

What is claimed is:
 1. A circuit assembly comprising: a heat-conductingbase plate; an insulating base; and a die having an integrated circuittherein, said die being in thermal contact with said heat-conductingbase plate, said heat-conducting plate being disposed between said dieand said insulating base.
 2. The circuit assembly of claim 1 whereinsaid insulating base further comprises a plurality of heat-conductingchannels, said heat-conducting channels being in thermal contact withsaid heat-conducting plate.
 3. The circuit assembly of claim 2 whereinsaid insulating base further comprises signal conducting channels forproviding electrical connections to said die, said heat-conducting platehaving an opening therein for making said connections between said dieand said conducting channels.
 4. The circuit assembly of claim 1 furthercomprising a heat-spreading cover in thermal contact with saidheat-conducting base plate, said heat-spreading cover overlying saiddie.
 5. The circuit assembly of claim 2 wherein said heat-conductingchannels comprise solder.
 6. The circuit assembly of claim 2 furthercomprising a solder protrusion extending from said heat-conductingchannels.
 7. The circuit assembly of claim 1 wherein saidheat-conducting base plate comprises copper.
 8. The circuit assembly ofclaim 1 wherein said heat-conducting plate is bonded to said insulatingbase.